Fix compile_resources present source directory

In certain scenarios, address the issue where gnome.compile_resources 
fails to transmit the present source directory. This is most notably 
visible with MSBuild.

examples/application4/meson.build

@@ -1,6 +1,6 @@
 app4_resources = gnome.compile_resources('exampleapp4_resources',
   'exampleapp.gresource.xml',
-  source_dir: '.')
+  source_dir: meson.current_source_dir())
 
 executable('exampleapp4',
   'exampleapp.c', 'exampleappwin.c', 'main.c', app4_resources,